Downhole pumping system

ABSTRACT

A downhole motor and pump assembly for use in a tube has a support that suspends the assembly downhole, a housing capable of forming a seal against an inside surface of the tube to divide the tube into a lower region below the seal and an upper region above the seal, an electric motor, and a power supply for the electric motor. A hydraulic pump driven by the electric motor has a high pressure output. A piston is operated by a directional valve such that the high pressure output from the hydraulic pump is directed by the directional valve alternately above and below the piston so as to reciprocate the piston. A fluid pump driven by the piston pumps well fluid from the lower region to the upper region.

This invention relates to a downhole pumping system, particularly for producing oil in a well.

When a borehole is extended to an oil formation, the oil in the formation is often under high pressure, and will be forced up the borehole without assistance. In some wells though, as the formation empties, the pressure drops and is insufficient to force the oil to the surface unassisted. Oil may also fail to rise under its only pressure when the well is very deep, and when the oil is viscous and has a high density.

Conventionally, a pump may be lowered down the well to assist the upward passage of oil where the pressure of the formation is not itself sufficient to bring the oil to the surface.

Further, in gas wells, gas flow can become impeded by fluid collecting in the bottom of the well. In such cases, it is known to install a pump in the well and pump the liquid to the surface, allowing the gas flow from the formation to resume.

The object of the present invention is to provide an effective arrangement of disposing a pumping system for such situations.

According to the present invention there is provided

-   -   a downhole motor and pump assembly for use in a tube, comprising     -   support means for suspending the assembly downhole,     -   a housing capable of forming a seal against the inside surface         of the tube to divide the tube into a region below the seal and         a region above the seal,     -   an electric motor,     -   power means to supply the electric motor,     -   a hydraulic pump driven by the electric motor and having a high         pressure output,     -   a piston operated by a directional valve, where the high         pressure output from the hydraulic pump is directed by the         directional valve alternately above and below the piston so as         to drive the piston in reciprocal motion, and     -   a fluid pump driven by the piston for pumping well fluid from         the region below the seal to the region above the seal.

Preferably, the high pressure outlet acts on a smaller area on one side of the piston than the other so that the piston operates with more force during one direction of its reciprocal motion than the other direction.

The invention will now be described, by way of example, with reference to the following drawings;

FIG. 1 shows a longitudinal section of the well bore as the motor and pump assembly;

FIG. 2 shows a diagrammatic representation of the control valve;

FIG. 3 shows a diagrammatic representation of the feed lines to the control valve;

FIGS. 4 a and 4 b show a longitudinal section of part of the pump and the control valve;

FIG. 5 shows another embodiment of the motor and pump assembly; and

FIGS. 6 a and 6 b show a further embodiment of the motor and pump assembly.

Referring to FIG. 1, there is shown a well bore which is lined with a casing 10. Inside this casing is a production tubing 20 through which fluid from the reservoir flows to surface. A retrievable standing valve assembly 53 (at bottom of tubing) having a one way valve 52 is located in a landing profile 54 at the bottom of the production tubing 20 by outward-pointing collet 56.

FIG. 1 also shows a motor and pump assembly 15 comprising a motor section 21 which rotates pump section 37 by means of a drive shaft 32.

The motor and pump assembly 15 is lowered down the production tubing 20 by a wireline 12. The wireline 12 also includes electrical conductors, which are attached to connectors 16 in the motor assembly top 14. The connectors 16 include a seal and can operate across high pressure difference (connectors supplied by Kemlon Products would be suitable for this purpose).

The electric conductors 18 pass down through a hollow channel 22 in a central fixed shaft 24, where they connect to stator windings in the dc brushless motor 15. The stator 27 is mounted on the shaft 24, and annular rotor 30 located around the stator 27 with bearings 26. A rotating hollow shaft 32 extends downwards from the annular rotor 30.

The central fixed shaft 24 includes a partition 11 which seals the volume in which the motor is disposed at its upper end. The rotating hollow shaft 32 is closed at its lower end, defining the lower extent of the volume. The volume is filled with motor oil, which is allowed to circulate e.g. up around the rotor and down between the rotor and stator. A movable annular piston head 19 is located below the partition 11, so that as the motor oil expands and contracts the pressure can be equalized, the volume above the piston head 19 being in communication with the fluid in the production tubing via ports 25.

The upper part of a connector sleeve 34 surrounds the lower part of the hollow shaft 32. The connector sleeve 34 and the hollow shaft 32 have corresponding magnetic coupling 28, 29, so that as the rotor 30 and hollow shaft 32 turn, the connector sleeve 34 is turned by the magnetic coupling with the hollow shaft 32. This allows the motor oil system 13 to be kept separate from the pump oil 17 surrounding the connector sleeve 34.

A hydraulic pump is located below the hollow shaft 32, the pump comprising interlocking gear wheels 35, 36, an axle 39, an inlet plate 38 and a outlet tube 40. Outer gear wheel 35 is secured to the inner surface of the lower part of the connector sleeve 34. The axle, inlet plate and outlet tube are fixed, so that as the connector sleeve rotates, the interlocking gear wheels also rotate, drawing fluid in through the inlet plate and forcing it at high pressure through the outlet tube.

A piston head assembly is located below the pump. A piston head 50 fits snugly against the inner surface of the motor and pump assembly housing 42. The piston head is mounted on co-axial inner and outer piston head tubes 45, 46. The inner tube 45 slidably extends into the outlet tube 40, and the outer tube 46 slidably abuts against an annular surface 48 which inwardly extends from the assembly housing 42. The piston head also includes a control valve. The operation of the control valve is described in more detail below, essentially though high pressure fluid from the hydraulic pump is expelled above the piston head to force the piston head down, then when the piston head reaches the end of its stroke the high pressure fluid is expelled below the piston head to force the piston head upwards, so that the piston head continuously reciprocates.

The hydraulic pump operates in a volume that is sealed by partition 71 at its upper extent, and by another partition 51 at its lower extent. A movable annular piston head 73 is located below the partition 71, so that as the motor oil expands and contracts the pressure can be equalized, the volume above the piston head 73 being in communication with the fluid in the production tubing via ports 72.

The piston head has a lower rod extending downwards through a dynamic seal in the lower partition 51. The lower rod terminates in a well fluid pump chamber 60 that fits against the inner surface of the motor and pump assembly housing 42 in a sealed, slidable manner. The well fluid pump chamber 60 has a one way valve 66, and upper outlet ports 65. The lower end of the motor and pump assembly housing 42 engages with the top of the standing valve assembly 53 in a sealed manner, so that the standing valve does not directly communicate with the annulus between the motor and pump assembly housing 42 and the production tubing 20.

The reciprocating movement of the piston head 50 in the motor and pump assembly housing 42 is transferred to the well fluid pump chamber 60 by the rod 62. As the well fluid pump chamber 60 rises from the bottom of its stroke to the top of its stroke near the partition 51, fluid is drawn from the region 70 below the standing valve, through the one way valve 52 into the region 75 in the motor and pump assembly housing 42 below the well fluid pump chamber 60. When the well fluid pump chamber 60 descends from the top of its stroke down to the bottom of its stroke near standing valve 50, the fluid in this chamber increases in pressure, closing the standing valve's one way valve 52. The increased pressure opens the one way valve 66 of the well fluid pump chamber 60, allowing fluid to flow into the chamber region 74 of the well fluid pump chamber 60, from there into the region 76 between the partition 51 and the well fluid pump chamber 60. When the well fluid pump chamber 60 starts a further ascent, fluid in the region 76 increases in pressure, the one-way valve 66 closes and the fluid is forced from the motor and pump assembly housing 42 into the annulus 78 between the motor and pump assembly housing and the production tube through exit ports 64.

In this manner, when fluid in a well no longer has sufficient pressure for it to be forced to the surface, the motor and pump assembly 15 may be lowered on a conducting wireline to the standing valve, and operated to pump fluid from below the standing valve into the production tube to the surface.

In order to get the maximum mechanical advantage from the hydraulic action of the piston head 50, the areas above and below the piston head are chosen to be as large as possible.

Referring to FIGS. 2 and 3, as previously mentioned, the piston head 50 includes a control valve 80 which is supplied with high pressure fluid to a port P1 by a tube 45, which may be directed to the volumes above or below the piston head (via ports P4 and P3 respectively). In order to accommodate displaced fluids, and to supply the hydraulic pump, another tube 46, concentric with tube 45, leads from a port P2. The control valve is shown in FIG. 2; The high pressure fluid supplied from port P1 is used to move the control valve against a spring between the two finite positions of the valve block (the details of the valve block and movement mechanism will be explained in more details below). In a first position, the high pressure fluid from port P1 exits through port P4 above the piston head 50, urging the piston head downwards. Fluid from below the piston head is allowed to pass through port P3 and exit to the reservoir through port P2. When the valve block is in the second position (i.e. pressurized fluid is no longer acting to push the valve block to the right in the figure, and the spring pushes the valve block to the left in the figure), the high pressure fluid applied at port P1 is directed to port P3 below the piston head, forcing the piston head 50 upwards. Fluid from above the piston head is allowed to flow through port P4 and directed by the control valve to the reservoir via port P2.

Typically, the high pressure fluid entering P1 will be 3000 psi. The pressure on the spool causing it to move will be in the order of 3500 psi.

Referring to FIGS. 4 a and 4 b, the piston head tubes 45, 46 support a circlip 90, which retains a set of Belleville washers 91 and an annular disc 92. The Belleville washers operate as an axial spring. The rod 62 between the piston head 50 and the well fluid pump chamber 60 also has a circlip 94, a set of Belleville washers 95 and an annular disc 96, arranged in the opposite manner to the flange, washers and disc of the piston head tubes 45.

The piston head 50 is disposed in a slidable sleeve 100 which can move with respect to the piston head. A link 104 is attached to the slidable sleeve at one end, and the spool 102 of the control valve 80_by pivot pins 103, 105 which engage in elongated slots 101, 106. The lever pivots around a pin 109 which is fixed in relation to the piston head 50. A spring 138 is constrained between the sleeve pivot pin 103 and the pin 109. The spool's pivot pin 105 can slide a short distance along the spool. Thus, downward movement of the sleeve 100 relative to the piston head tends to move the spool 102 upwards into the piston head, but the spool's pivot pin 105 and the elongate slots that the pivot pins engage with allows some freedom between the sleeve 100 and the spool 102.

The co-axial inner and outer tubular piston head tubes 45, 46 supply a reservoir feed 110 which accepts fluid displaced from the cylinder, and a high pressure feed from the hydraulic pump 111. The spool has upper and lower lands 112, 114, and sits in a bore having upper and lower chambers 116, 118 for the lands. The lands may have upper and lower chamfered surfaces, with the chambers having a corresponding chamfer at each end. The reservoir feed 110 and the high pressure feed 111 enter the upper and lower chambers 116, 118 at the center of each chamber. An above piston head feed line 120 (corresponding to P4 in the generalized discussion of the hydraulics) leads from the upper face of the piston head to the upper part of the upper chamber 116 and the lower part of the lower chamber 118. A below piston head feed line 122 (corresponding to P3 in the generalized discussion of the hydraulics) leads from the lower face of the piston head to the lower part of the upper chamber 116 and the upper part of the lower chamber 118.

In FIG. 4 a, high pressure fluid supplied from the hydraulic pump through the high pressure feed 111 is fed into the upper and lower chambers 116, 118, where it is directed by the spool 102 to the below piston head feed line 122 and thence to below the piston head 50. This action forces the piston head to rise, so that fluid from above the piston head is forced through the below piston head feed line 122 to the lower part of the upper chamber 116 and the upper part of the lower chamber 118, and thence into the reservoir feed line and on to the reservoir itself.

As the piston head rises, the upper end of the sleeve 100 presses against the annular disc 92 and Belleville washers 91, compressing the washers, but the piston head starts to move upwards relative to the sleeve until lower inwardly pointing collet 130 on the sleeve 100 engages with the lower surface of the piston head. The bore in which the spool sits includes a biased ball bearing 125, which engages with an upper hollow 126 on the spool. This engagement resists movement of the spool, so initially, freedom in the link system accommodates the movement. As the piston head reaches the top of its stroke and the Belleville washers are at their maximum compression, the upward force on the spool is sufficient to overcome the biased ball bearing and the spool moves upwards in the bore. The link over-centers as the sleeve is pushed quickly downwards by the expanding Belleville washers, the inwardly pointing collets 130 engaging with the top of the piston head 50; the constrained spring 138 also helping to over-center the link. The ball bearing engages with a lower hollow 127 on the spool. Additionally, the spool may include a channel 136 running along its length which has an opening at the upper end in a chamber 135 above the spool, and an opening 137 towards the lower end of the spool. In either spool position, the lower end opening 137 communicates with the region below the piston head, so that the pressure above and below the spool is equalized and the region below the piston head does not exert a net force on the spool.

It will be seen that the arrangement of ports in the upper and lower chambers 116, 118 ensures that the force on the upper land caused by the difference in the high pressure fluid and the low pressure fluid is exactly balanced on opposite force on the lower land.

Referring to FIG. 4 b, the biased ball bearing engages in a lower hollow 127, stopping further movement of the spool. Fluid from the high pressure feed 111 upper and lower chambers 116, 118, is now directed by the spool 102 to the above piston head feed line 120, forcing the piston head downwards, aided by the stored energy in the Belleville washers.

Fluid from below the piston head is now forced through the below piston head feed line 122 and directed by the spool into the reservoir feed line. The process describing the rise of the piston head is now reversed. Thus the output of high pressure fluid from the hydraulic motor is converted into reciprocating motion.

The force provided by the Belleville washers and the link spring 138 ensures that spool is switched quickly between its first position and its second position; it will be realized that one could rely solely on the Belleville washers or solely on the link spring, or indeed use another mechanism to ensure that the spool switches swiftly between its two positions.

In the example described above, greater work is done by the piston head during the upstroke, when the well fluid pump chamber 60 is raised. The pump may be arranged so that the greater work of the cycle is carried out during the piston head's downstroke. Referring to FIG. 5, the piston head 50 has a lower tube 140 extending downwards through a dynamic seal in the lower partition 51. The lower tube extends through a pump cylinder 141 and terminates in a one way valve 142 located in pump cylinder chamber 143. A compression spring biases against the one way valve.

In operation, as the piston head 50 moves upwards, the lower tube 140 is raised and fluid flows through the one way valve 142, priming the pump. On the piston head's downstroke, the one way valve 142 closes, so that fluid previous drawn into the lower tube is expelled into region 76 and out through ports 64. In this embodiment, the pump's work is chiefly expended on the piston head's downstroke, as opposed to the previous embodiment, where the work of the pump is operated in the chiefly expended on the piston head's upstroke.

In order to get the maximum mechanical advantage from the hydraulic action of the piston head 50, the area of the upper surface of the piston head 50 is designed to be as large as possible (with the outer diameter of the piston head tubes 45, 46 being as chosen to be as small as possible). Similarly, the outer diameter of the lower tube 140 is chosen to be as large as possible. Typically, the lower tube will be 2.5 cm, and have a long stroke.

The hydraulic system may further be arranged to exert a much greater force on one stroke direction than the return stroke. Referring to FIG. 6, a piston head has an upper portion 146 and a lower portion 148 separated by a middle portion 147 which has a greater diameter than either the upper or lower portions 146, 148 and seals against the inner surface of the housing 42. The upper portion is wider than the lower portion. Hydraulic fluid is supplied to the piston head by a tube 40 which is dynamically sealed to the hydraulic pump's outlet. As the shuttle valve in the piston head operates, high pressure fluid is directed alternately to the annulus 152 around the lower portion 148 and the annulus 150 around the upper portion 146 (the shuttle valve operating in the manner previously described). In FIG. 6 a, the high pressure fluid in the annulus 152 is acting on the upper surface of the middle portion 147 and has forced the piston head to the top of its stroke. In FIG. 6 b, the high pressure fluid is directed to the annulus 150, and acts on the lower surface of the middle portion 147 and to move the piston head downwards. Since the upper surface of the waist is a much smaller area than the lower surface of the waist, the up stroke of the piston head has more force than the down stroke.

The lower portion of the piston head extends into a lower region 76, and terminates in a plunger and one way inlet valve 154. As the piston head 50 descends, the plunger also descends and the one way valve opens, allowing fluid to flow above the plunger. In addition to the standing valve, a check valve 156 may be included in the housing port 64 to hold the column of fluid in the production tube above the motor and pump assembly. When the piston head then ascends and the plunger is drawn up, the one way valve 154 closes and the fluid above the plunger is expelled out of the check valve. It will be seen that by virtue of the shape of the piston head, more force is exerted on the upward stroke when it is necessary to expel water into the fluid column of the production tube, than on the plunger's down stroke when the valve is open. If the well contains gas as well as fluid, gas entering the region between the a traveling valve such as the one way valve 154, and one of the stationary valves such as the standing valve's one way valve 52 or the check valve 156, the pump can become gas locked when the gas fails to open the outlet valve during the compression stroke. By providing a very high compression ratio, the gas achieves a sufficient pressure to open the outlet valve, unlocking the pump. 

1. A downhole motor and pump assembly for use in a tube, the assembly comprising support means for suspending the assembly downhole, a housing capable of forming a seal against an inside surface of the tube to divide the tube into a lower region below the seal and an upper region above the seal, an electric motor, power means for supplying the electric motor, a hydraulic pump driven by the electric motor and having a high pressure output, a piston operated by a directional valve such that the high pressure output from the hydraulic pump is directed by the directional valve alternately above and below the piston so as to reciprocate the piston, and a fluid pump driven by the piston for pumping well fluid from the lower region to the upper region.
 2. The assembly according to claim 1 wherein the high pressure outlet acts on a smaller area on one side of the piston than the other so that the piston operates with more force during one direction of its reciprocal motion than the other direction.
 3. The assembly according to claim 1 wherein the directional valve is housed in the piston.
 4. The assembly according to claim 1 wherein the piston is connected to the hydraulic pump by a slidable tube which moves with the piston.
 5. The assembly according to claim 1 wherein the directional valve includes a spool that switches between two positions during a cycle of the piston.
 6. The assembly according to claim 5 wherein the spool is switched by the relative movement of the piston and a collet located around the piston.
 7. The assembly according to claim 1 wherein energy storing and releasing means such as springs are associated with the piston to assist the piston's movement and the switching of the spool.
 8. The assembly according to claim 1 wherein the fluid pump operates at a compression ratio of 80:1 or higher. 